1. Field of the Invention
The present invention relates to a control apparatus and a control method for an internal combustion engine having a turbocharger, and more particularly to control of an exhaust bypass valve such as a wastegate valve.
2. Description of the Related Art
A turbocharger installed with an exhaust turbocharger that is operated by rotating a turbine using exhaust gas is available as conventional means for improving the output of an internal combustion engine (referred to as an engine hereafter) and so on.
In this type of turbocharger, when the engine performs a high rotation/high load operation, a supercharging pressure may increase excessively, and as a result, the engine may be damaged. Therefore, an exhaust bypass passage is normally provided parallel to the turbine.
A control apparatus for an internal combustion engine having the turbocharger and exhaust bypass passage described above adjusts an amount of exhaust gas flowing into the turbine by diverting a part of exhaust gas flowing through an exhaust gas passage to the exhaust bypass passage using a wastegate valve provided in the bypass passage. As a result, the supercharging pressure, i.e. the pressure in an intake passage of the engine, can be controlled to an appropriate value.
The wastegate valve is operated to open and close by driving a positive pressure actuator, for example. More specifically, the wastegate valve is configured such that an opening thereof is adjusted by driving the positive pressure actuator particularly in an operating condition where the pressure in a part of the intake passage upstream of a throttle valve used to increase the pressure is higher than atmospheric pressure.
In a period before the positive pressure actuator can be driven, the wastegate valve is normally fully closed. Note that hereafter, the wastegate valve will be referred to as a WGV, and a wastegate valve actuator for operating the WGV will be referred to as a WGA.
The positive pressure actuator can operate the WGV only when the pressure in the intake passage of the engine is higher than a threshold. In other words, when the pressure in the intake passage of the engine is equal to or lower than the threshold, the WGV cannot be operated, and therefore the opening of the WGV cannot be modified.
Hence, a system in which the WGA is electrified so that the WGV can be driven as required, regardless of the pressure in the intake passage of the engine, has recently been proposed so that turbocharging by the turbocharger can be limited more freely.
In this system, however, an error arises between a detection value of a WGV opening sensor and a true WGV opening due to factors such as temporal variation occurring as the WGV is opened and closed repeatedly for a long period of time, a temperature characteristic of the WGV opening sensor, and thermal expansion of structures constituting the WGV.
As a result, a “reference position of the WGV”, which corresponds to a position of the WGV when the detection value of the WGV opening sensor is 0%, deviates from a “fully closed position of the WGV”, which corresponds to the position of the WGV the when the true WGV opening is 0%.
Hence, a deviation may occur in the WGV opening even when the WGA is operated by identical operation amounts, and as a result, it may be impossible to control the WGV to a desired open/closed condition. Moreover, the supercharging pressure may not reach a control target value, or conversely, control may be executed to attempt to operate the WGV further toward the closed side from a fully closed condition, causing a drive current of the WGA to form an overcurrent.
In a conventional technique proposed in response to this problem, when the WGV converges on the fully closed position, the fully closed position is learned on the basis of an output value of the opening sensor at that time (see Japanese Patent Application Publication No. 2015-59549, for example). According to Japanese Patent Application Publication No. 2015-59549, in a situation where there are few opportunities for learning or the WGV does not converge on the fully closed position, the learned fully closed value is corrected to a value taking into account variation in a sensor output characteristic in accordance with temperature variation occurring from the point at which the learned fully closed value is updated. As a result, with Japanese Patent Application Publication No. 2015-59549, control precision can be maintained with stability in a WGV mechanism even when a temperature condition varies.